This invention relates in general to the field of semiconductor device fabrication, and more particularly to a method and system for dispensing process gas for fabricating a device on a substrate.
Microelectronic devices, such as integrated circuit (IC) chips formed on a semiconductor substrate wafer, have grown increasing complex over the past several years. By miniaturizing the circuits of the microelectronic devices, industry has achieved significant performance improvements in terms of increased processing speed and decreased footprint. However, the miniaturized circuits are difficult to form. Minor contamination by impurities and other imperfections have greater and greater effects on the integrity of the devices as the size of circuits within microelectronic devices decrease. As industry transitions from the present 0.25 micron circuit devices to devices having smaller circuits, such as 0.18 and 0.13 microns, device formation techniques will have to provide greater precision using a wider variety of materials and with decreased contamination of the device. One example of a new material designed to reduce device size is the use of copper instead of aluminum to form device interconnects.
Microelectronic devices can be formed on substrates in a number of different ways. Some conventional techniques for forming microelectronic devices include rapid thermal processing (RTP), etch processing, and physical vapor deposition (PVD). PVD occurs in a relatively low pressure environment. A target, comprised of the material to be deposited, and the substrate are disposed in a reaction process chamber with a low pressure plasma gas. The target deposits the material on the substrate by the creation of an electric charge difference between the target and the substrate.
Chemical vapor deposition (CVD) is another example of a conventional and well-known process for depositing materials on a substrate to fabricate a microelectronic device on the substrate, such as in the fabrication of a semiconductor IC chip. To achieve a uniform growth of a thin-film material on a substrate, conventional CVD systems attempt to distribute a precursor gas, sometimes in combination with other reactant gases, in a uniform flow over the substrate. Under predetermined conditions for the precursor, such as predetermined temperature and pressure conditions within the CVD reaction process chamber and the substrate, the precursor deposits a desired material on the substrate as the precursor flows over the substrate. For instance, CVD provides excellent thin-film deposition of copper, tantalum nitride, titanium nitride, barium strontium titanate, and other materials typically used as thin-films for device fabrication on a substrate.
PVD and CVD provide different advantages based upon the material to be deposited. For example, CVD provides significant advantages in the deposition of a uniform thin-film of copper on a substrate. However, it is difficult to manufacture microelectronic devices by combining PVD and CVD processes due to the relatively high pressure of the process gas used in the reaction process chamber for CVD compared to the low pressure used for PVD. Further, the gases used to support CVD tend to damage substrates if the CVD gases are inadvertently introduced during a PVD process.
Typically, CVD occurs in a reaction process chamber that provides a low-conductance, contaminant-free environment for flowing the precursor over the substrate in a uniform manner. Alternatively, CVD can be performed in a high-conductance reaction process chamber that provides a relatively large flow of process gas to achieve a uniform film deposition. High-conductance systems generally have a larger footprint than do low-conductance systems, and use a greater amount of process gas for a given film deposition thickness. After deposition, the precursor is evacuated from the reaction process chamber to allow deposition of a subsequent material film, or to allow transfer of the substrate to another reaction process chamber for deposition of the subsequent material film. CVC, Inc. has a hub system that connects a number of reaction process chambers through a central hub to allow transfer of the substrate. The central hub is maintained at a low pressure to minimize the introduction of contaminants during transfer of substrate wafers through the hub.
Conventional single wafer CVD systems feed gases above and perpendicular to the substrate wafer. The gases deflect from the center of the wafer and flow radially from the center to an exhaust port located below the substrate wafer. In such conventional systems, the center of the substrate tends to receive a higher concentration of process chemicals associated with the gases, resulting in faster thin-film material growth at the center of the substrate than at the edges. This can lead to a bell-shaped film thickness with a thicker film at the center of the substrate than at the edge.
To alleviate this difficulty, conventional CVD systems use a showerhead arrangement. The precursor gas flows from above the showerhead into a centrally-located inlet of the showerhead housing. The showerhead housing has a showerhead gas dispersion plate with several hundred small openings to allow a low-conductance flow of the precursor gas to the CVD reaction chamber for more-uniform distribution across the substrate. To encourage a uniform distribution of the precursor gas from the dispersion plate openings, a deflector plate is typically disposed between the incoming gas flow and the dispersion plate. The deflector plate deflects the incoming gas flow radially from the intake vector to fill the showerhead housing with gas before the gas flows through the openings, thus avoiding an excessive concentration of gas flow over the center of the substrate.
Although a deflector plate and showerhead in a conventional CVD system can aid in the relatively uniform distribution of gas across the substrate, this arrangement creates a number of difficulties in the commercial production of microelectronic devices on a substrate wafer. For instance, the process gas inlet at the top of the showerhead increases the height footprint of the system and vertical thickness of the showerhead housing. This can increase the amount of precursor gas needed for deposition of a given film. Further, the inlet and associated fittings increase the difficulty of showerhead maintenance, and the likelihood of contamination during CVD processing. For example, to allow servicing of the showerhead, flexible hoses are often used between the showerhead inlet and process gas source. These hoses impede access to the showerhead housing, and can include particulate contaminates that can break free during CVD processing to introduce contaminants to the substrate.
Another difficulty associated with conventional CVD systems relates to system throughput. During CVD processing, gases are distributed from the showerhead inlet, through the dispersion plate and across the substrate with a low-conductance uniform flow. After deposition of the desired film, gas flow through the inlet is ceased by a shutoff valve, and residual gases are removed from reaction chamber through an exhaust located at the bottom of the reaction chamber. This results in process gas flowing over the entire length of the reaction chamber. Once the residual gas is removed from the reaction chamber, the substrate can be removed from the reaction chamber for further processing. For instance, the hub system sold by CVC, Inc. can move the substrate between several reaction chambers through a central hub, thus minimizing contamination of the substrate between the deposition of different material layers in separate reaction chambers.
To minimize contamination of the hub and associated reaction chambers during substrate handling, a thorough evacuation of residual gases upon completion of a deposition process is generally accomplished before transfer of the substrate through the hub. The low conductance of the reaction chamber and showerhead dispersion plate openings tends to increase the time needed to evacuate the reaction chamber since the evacuation pump has to draw residual process gas through the openings for evacuation of the showerhead housing. In low-conductance systems, baffles associated with the reaction chamber also impede evacuation of residual gas. Further, even with an extensive evacuation time, residual gas typically remains in the precursor delivery line, the showerhead housing and the reaction chamber, resulting in plating of material from the precursor on the wafer handling system, such as the wafer chuck, when the residual gas decomposes, and eventual contamination of the system. Increased evacuation time can decrease the presence of residual gas, but even extensive evacuation times generally cannot eliminate the residual gas from the showerhead and reaction chamber before transfer of the substrate wafer through the hub. The increased evacuation times lead to a corresponding decrease in system throughput.
Another difficulty of conventional CVD systems results from CVD processes that use two or more gases to deposit a material on a substrate. For instance, a precursor and reducing gas chemically support deposition of a material on a substrate, but are chemically incompatible if mixed before delivery to the substrate. If the precursor and reducing gas are mixed in the delivery line or showerhead housing before flowing to the reaction chamber, they will generate particles that cause blockage of the gas delivery system and that can cause undesired composition of the film material.
One conventional technique for delivery of plural gases without premixing is to use a multi-zone showerhead. The incompatible gases are fed into separate rings in the showerhead housing for delivery to the reaction chamber by separate concentric zones of dispersion plate openings. However, the multiple zones typically result in the deposited film having a ring pattern similar to the pattern of the zones of the dispersion plate. Multiple zones designed with smaller zones to minimize the ring-pattern of the deposited film also have an increased resistance to flow in each zone. The increased flow resistance decreases system throughput by increasing pumping and purging cycle times and can cause condensation of pressure-sensitive precursor vapor.
Further, the multi-zone showerhead design is difficult to manufacture and inflexible with respect to its use with various combinations of gases, flow rates and reactor geometries.
Another difficulty associated with CVD relates to the deposition of the material from the precursor gas to the reaction chamber walls and to the chuck-that supports the substrate in the reaction chamber. CVD of a copper film presents increased difficulty due to the narrow range of conditions in which the copper precursor is stable. For instance, one typical copper precursor will decompose at temperatures above 100 C, and will condense at temperatures below 50 C. Thus, over a series of CVD depositions, a reaction chamber and chuck used for copper deposition tends to have a residual film of copper build, which can interfere with subsequent depositions.
Therefore a need has arisen for a method and system which supports increased throughput of uniform thin film deposition of a material on substrates for device formation on the substrates.
A further need exists for a method and system that supports low-conductance process gas flow in a reaction chamber for chemical vapor deposition and highconductance process gas flow for evacuation of the reaction chamber after deposition.
A further need exists for a method and system which supports increased throughput of uniform thin film deposition of multiple material layers for device formation using chemical vapor deposition of one or more layers and physical vapor deposition of one or more layers.
A further need exists for a method and system which supports deposition of a material for device formation on a substrate in a reaction chamber using a process gas with reduced evacuation time for the evacuation of the process gas from the reaction chamber after deposition is complete.
A further need exists for a method and system which supports deposition of a film on a substrate having a precise and uniform thickness by a process gas without deposition of the film on the chuck supporting the substrate.
A further need exists for a method and system which provides rapid evacuation of residual gas from a chemical vapor deposition showerhead after completion of the deposition of a film with the gas.
A further need exists for a method and system which dispenses process gas into a reaction chamber using a reduced footprint.
A further need exists for a method and system which supports increased throughput of uniform thin film deposition of a material for device formation on a substrate using plural process gases, such as chemical vapor deposition with plural reaction gases.
A further need exists for a method and system which allows increased flexibility in the configuration and maintenance of equipment used for deposition of material layers using process gases, such as by chemical vapor deposition of a material.
A further need exists for a method and system which reduces the presence of contaminants during deposition of a material as a thin film for device formation on a substrate using a process gas, such as by chemical vapor deposition of a material.
In accordance with the present invention, a method and system are provided that substantially eliminate or reduce disadvantages and problems associated with previously developed methods and systems for deposition of a uniform thin film of a material for device formation on a substrate.
The method and system according to the present invention use a reaction chamber that contains a heated substrate support chuck for supporting and heating a substrate during deposition of a material film. The reaction chamber accepts process gas to support deposition of the material, and has an exhaust port for evacuating the process gas as needed. For instance, CVD process gas flows from a showerhead, over the substrate and then out the exhaust port. The reaction chamber has a low-conductance configuration to provide an axisymetric process gas flow over the substrate during deposition, and a high-conductance configuration to provide enhanced evacuation of the reaction chamber after the completion of deposition. The low-conductance configuration provides optimal process gas flow to enhance the deposition of a uniform film on the substrate, and the high-conductance configuration enhances process throughput by reducing the post-process evacuation time.
More specifically, one embodiment of the present invention uses the position of the chuck relative to the exhaust port to provide a low-conductance configuration during deposition of a material by a process gas, and to provide a high-conductance configuration during evacuation of residual gas after deposition of the material by the process gas. The exhaust port is located along a side wall of the reaction chamber. An actuator or adjusting motor positions the chuck in substantial alignment with the exhaust port to support, so that the chuck restricts the flow path from the showerhead to the exhaust port, to support a low-conductance configuration for deposition with the process gas. To support a high-conductance configuration for evacuating the reaction chamber, the chuck is position away from the showerhead and exhaust port to avoid impedance of the flow of process gas from the reaction chamber to the exhaust port.
The chuck has a support region for supporting the substrate wafer proximate the showerhead, a backside region on the opposite side that faces the backside of the reaction chamber, and an indented region formed between the support region and the backside region. In the low conductance configuration, the support region and backside region form a gap next between the chuck and the reaction chamber walls. The gap formed by the support region restricts process gas flow from the showerhead to the exhaust port, and the gap formed by the backside region restricts the flow of process gas to the backside of the reaction chamber. The indented region provides a channel in substantial alignment with the exhaust port to allow process gas to flow through the support region gas in a uniform, axisymetric flow. The channel directs process gas flow from the indented region to the exhaust port for evacuation. In the high conductance position, the chuck has openings in the support and backside region to enhance evacuation of residual gas from the backside of the reaction chamber and from the indented region is through the exhaust port. The chuck includes a thermal energy distribution apparatus to provide precise control of the temperature across the substrate wafer according to predetermined deposition conditions, and to reduce deposition of the material on the chuck by maintaining the chuck at temperatures that limit deposition.
An alternative embodiment of the present invention uses plural evacuation openings to provide a highconductance configuration during evacuation of residual gas after deposition of the material by the process gas. For instance, an evacuation opening is provided in the showerhead housing to allow direct evacuation of the showerhead without evacuating the residual gas through the low-conductance gas dispersion plate. In conjunction with evacuation of the housing, purge gas is provided through the process gas feed to purge residual gas from the process gas feed line and to help force residual gas from the housing.
Another embodiment of the present invention provides improved process gas dispersion using a reduced footprint. A showerhead housing accepts a reactant gas, such as a precursor for chemical vapor deposition of a material, through a reactant gas inlet opening located on the side of the housing. The reactant gas enters the housing through the side opening along a flow vector that is generally parallel to the exposed upper surface of a substrate disposed in a reaction process chamber associated with the housing. A baffle is disposed in the housing proximate the inlet opening for redirecting the flow vector of the gas to an outflow vector that is generally perpendicular to the surface of the substrate. The reactant gas flows along the outflow vector through a gas dispersion plate to uniformly flow over the substrate, allowing the reactant gas to deposit a desired material on the substrate surface.
In an alternative embodiment, the showerhead housing can accept plural separate gas flows through plural process gas feed openings located on the side of the housing. A first process gas flows into a first plenum disposed in the showerhead housing. A second process gas flows into a second plenum disposed in the showerhead housing. A baffle associated with each plenum redirects the respective process gas flow to an outflow vector for dispensing to the substrate. Passageways provide a flow path for the first process gas to flow from the first plenum, through the second plenum and into the reaction chamber without mixing with the second process gas flow until both process gas flows enter the reaction chamber. The passageways feed the first process gas flow to openings of a gas dispersion plate for dispensing the flow to the reaction chamber. The second process gas flow passes through openings in the gas dispersion plate and into the reaction chamber. The openings associated with passageways and the openings associated with the second plenum are arranged in geometric patterns that correlate to a desired flow pattern. The geometric patterns can include squares, triangles, hexagons and octagons.
The present invention provides important technical advantages for the deposition of a uniform thin film of a material on a substrate to form a device using chemical vapor deposition. One important technical advantage is the greater throughput of the present invention. Increased throughput is provided by reduced purge and evacuation cycles needed to remove residual process gas from the reaction chamber.
Another important technical advantage is the combined high-conductance and low-conductance configurations available with the present invention. Low-conductance provides uniform axisymetric process gas flow over the substrate with a reduced footprint and reduced usage of process gas. High-conductance allows rapid evacuation of residual gas upon completion of a deposition cycle. The combination of a low and high conductance configuration in a single system provides the advantages of both types of deposition, leading to greater throughput and reduced risk of contamination by residual gas.
Another technical advantage of the present invention is an enhanced capability to combine CVD and PVD reaction chambers along a single hub system. The improved evacuation of residual gas provided by the present invention allows substantially complete removal of residual gas from the reaction chamber and showerhead in a time period that makes throughput of combined PVD and CVD chambers economically feasible.
Another technical advantage of the present invention is the precise control of substrate thermal levels to enhance uniform film deposition across the substrate without deposition on the chuck.
Another technical advantage of the present invention is the reduced evacuation time provided by direct evacuation from the showerhead housing without evacuation of residual gas through the gas dispersion plate. By allowing evacuation of residual gas from both the reaction chamber and the showerhead housing, the present invention reduces the time needed to purge the system in support of wafer handling for further deposition processing.
Another important technical advantage of the present invention is the reduced footprint of the showerhead housing achieved by the side feed of process gas. Reduced footprint can mean substantial savings by allowing room for a greater amount of equipment in the expensive clean rooms used to produce microelectronic devices. Further, feeding process gas to the side of the housing provides improved accessibility for maintenance of the showerhead, and reduced risk of contamination breaking free from flexible hose assemblies.
Another technical advantage of the present invention is the ability to provide a uniform mixture of plural process gases to the reaction chamber without mixing the gases in the housing. The geometric shapes of the openings associated with separate plenums for separate process gas flows enables uniform flow and mixture of the process gases to the reaction chamber. The uniform flow and mixture reduces ring-shaped deposition on the substrate and allows precise control of process gas flows.
Another technical advantage is that games are fed from an enclosed, vented gas box into the showerhead in a safe manner. For instance, all connections can be xe2x80x9cdual containedxe2x80x9d connections to limit dangers related to gas leakage. Any leakage of toxic gas at these connections can be scavenged by differential pumping and safely removed.